The in-situ delivery of therapeutic agents within the body of a patient is common in the practice of modern medicine. In-situ delivery of therapeutic agents is often implemented using medical devices that may be temporarily or permanently placed at a target site within the body. These medical devices can be maintained, as required, at their target sites for short or prolonged periods of time in order to deliver therapeutic agents to the target site.
In some cases however, delivery of the biologically active material to the body tissue immediately after insertion or implantation of the medical device may not be needed or desired. For instance, if a stent is used to prevent the occurrence of restenosis after balloon angioplasty, it may be desirable to ensure that the drug continues to be released when restenosis occurs or begins to occur in a body lumen that has been stented with a drug-coated stent. Therefore, there is a need for insertable or implantable medical devices that can provide delayed and/or controlled, continuous delivery of biologically active materials when such materials are required by the patient after implantation of the medical device.
Current techniques for the in-situ delivery of therapeutic agents in a controlled manner often involve the use of a polymer coating on the insertable or implanatable medical device to contain the agents and control its release rate. The polymer coating, however, may sometimes be a contributing factor in causing an inflammatory response in the tissue with which it comes in contact. For instance, when a Drug Eluting Stent (DES) is implanted in a vessel, the inflammatory response which sometimes arises can cause a reduction in the diameter of the vessel lumen within the stent. The inflammatory response can lead to late in stent thrombosis.